In recent years, with the advances in semiconductor miniaturization technologies, densities and capacities of memory devices (memories) have been significantly increased. The field of nonvolatile memory devices has made remarkable technological developments (such as miniaturization) in flash memories and electrically erasable and programmable ROMs (EEPROMs), and thus begun to achieve cost reduction. However, the miniaturization of flash memories is said to be approaching the limit. With this being the situation, a new nonvolatile memory device has received attention for further reducing a cell area size and a cost.
Research and development have been promoted for a nonvolatile memory device, as the new nonvolatile memory device, having a memory cell including a variable resistance element. Here, the variable resistance element reversibly changes a resistance value in response to an electrical signal, and can store data corresponding to this resistance value in a nonvolatile manner.
As a nonvolatile memory device employing a variable resistance element, a 1T1R nonvolatile memory device is generally known. This 1T1R nonvolatile memory device has a structure where so-called 1T1R memory cells are arranged in an array of a matrix. Each of the 1T1R memory cells includes a metal oxide semiconductor (MOS) transistor and a variable resistance element that are connected in series at a position near a cross point of a bit line and a word line that are arranged to cross each other. Moreover, as another example, a cross point nonvolatile memory device is also generally known (see Patent Literatures 1 and 2, for instance). This cross point nonvolatile memory device has a structure where so-called 1D1R memory cells are arranged in an array of a matrix. Each of the 1D1R memory cells includes a diode serving as a current steering element in place of a transistor.
Patent Literature 1 discloses a 1D1R nonvolatile memory device that employs, as a memory cell, a variable resistance element having a characteristic of changing resistance bidirectionally. Moreover, Patent Literature 2 discloses a 1D1R memory cell that employs a unidirectional variable resistance element as a memory cell.